(1) Field of the Invention
The present invention relates to organic crystal films and more particularly to organic crystal films for nonlinear-optics applications.
(2) Background Information
Increasing bandwidth has become an increasingly pressing requirement of modem communications systems. As fiber optics replaces electrical cabling, WDM and DWDM techniques are used to exploit a greater fraction of the available fiber optic bandwidth. Simultaneously, packet-switched signal architectures are gradually replacing TDM techniques in many application sectors. However, despite the impressive resources invested in these efforts to expand bandwidth, one significant bottleneck remainsxe2x80x94switching node (interconnect) hardware. Current interconnection devices typically require the data to be first converted to an electrical signal, routed to the correct output, and then re-converted to an optical signal. This opto-electronic interface introduces latencies and substantially reduces the overall bandwidth of the system. All-optical (i.e., without opto-electronic conversion) switching technologies utilizing MEMS (microelectromechanical system) or polarization-based technologies may preserve the fiber bandwidth but tend to switch slowly, introducing latencies that limit their applicability.
Nonlinear optical (NLO) materials offer rapid switching speeds. However, a need exists for improved performance while overcoming the drawbacks associated with current NLO materials. For example, devices using inorganic NLO crystals such as titanium-diffused lithium niobate (Ti:LiNbO3) tend to have inferior performance due to their weak NLO properties. In addition, temporal and thermal stability as well as radiation sensitivity are well-known problems. Furthermore, these conventional inorganic crystal devices are relatively difficult to integrate directly with electronics.
NLO devices based on thin films of poled organic polymers may be a viable solution, since such organic materials are low cost and readily processed. Hundreds of nonlinear organic materials have been synthesized and characterized, and devices using such materials have been demonstrated. However, these poled polymers tend to have the following disadvantages: small second-order susceptibility, low optical damage threshold, high scattering losses, and limited temperature and temporal stability. Thus, poled NLO polymers still require a breakthrough in development to achieve practicality, despite the inherent advantages of the organic materials.
One way of taking advantage of thin film organics while potentially overcoming these limitations is using NLO organic crystal films, which have tend to have a very high optical nonlinearity, higher damage threshold, and low scattering loss. Hattori et al., in U.S. Pat. No. 5,385,116, has reviewed various techniques for fabricating organic crystal films. However, significant manufacturability issues for practical devices generally remain. Until, and unless these problems are solved, the inherently superior organic NLO crystal materials likely will not realize their potential.
Therefore there exists a need for an improved optical film that exhibits large nonlinear optical effects while overcoming drawbacks of film devices.
One aspect of the present invention includes a method for fabricating a crystalline, non-linear optical (NLO) film. The method includes providing a substrate, an alignment layer material including elongated polymeric molecules, and at least one NLO material. The method further includes depositing a thin layer of the alignment layer material on at least one surface of the substrate, aligning the molecules of the alignment material in a substantially uniaxial direction, and depositing a layer of the at least one NLO material on the alignment layer material. In another aspect, this invention includes a film structure fabricated by the method described hereinabove in this paragraph.
In a further aspect, this invention includes a method for fabricating a crystalline NLO film. The method includes providing a substrate, an alignment layer material including elongated polymeric molecules, and at least one NLO material. The method further includes depositing a thin layer of the alignment layer material on at least one surface of the substrate, aligning the molecules of the alignment layer material in a substantially uniaxial direction, depositing a seed layer of one of the at least one NLO material on the alignment material, and depositing another layer of one of the at least one NLO material on the seed layer. In a still further aspect, this invention includes a NLO film structure fabricated by the ma described hereinabove in this paragraph.